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A workflow describes how certain entities have to evolve between different
states. Hence we have a set of states, and a “transition graph”, i.e. a set of
possible transitions from one state to another state.

We will define a simple workflow for a blog, with only the following two states:
submitted and published. You may want to take a look at Building a simple blog with CubicWeb if
you want to quickly setup an instance running a blog.

We want to create a workflow to control the quality of the BlogEntry
submitted on the instance. When a BlogEntry is created by a user
its state should be submitted. To be visible to all, it has to
be in the state published. To move it from submitted to published,
we need a transition that we can call approve_blogentry.

A BlogEntry state should not be modifiable by every user.
So we have to define a group of users, moderators, and
this group will have appropriate permissions to publish a BlogEntry.

There are two ways to create a workflow: from the user interface, or
by defining it in migration/postcreate.py. This script is executed
each time a new cubicweb-ctldb-init is done. We strongly
recommend to create the workflow in migration/postcreate.py and we
will now show you how. Read Two bits of warning to understand why.

The state of an entity is managed by the in_state attribute which
can be added to your entity schema by inheriting from
cubicweb.schema.WorkflowableEntityType.

This will create an entity of type Transition with name
approve_blogentry which will be linked to the State entities
created before.

add_transition expects

as the first argument: the name of the transition

then the list of states on which the transition can be triggered,

the target state of the transition,

and the permissions
(e.g. a list of user groups who can apply the transition; the user
has to belong to at least one of the listed group to perform the action).

checkpoint()

Note

Do not forget to add the _() in front of all states and
transitions names while creating a workflow so that they will be
identified by the i18n catalog scripts.

In addition to the user groups (one of which the user needs to belong
to), we could have added a RQL condition. In this case, the user can
only perform the action if the two conditions are satisfied.

If we use an RQL condition on a transition, we can use the following variables:

X, the entity on which we may pass the transition

U, the user executing that may pass the transition

You can notice that in the action box of a BlogEntry, the state is now
listed as well as the possible transitions for the current state
defined by the workflow.

The transitions will only be displayed for users having the right permissions.
In our example, the transition approve_blogentry will only be displayed
for the users belonging to the group moderators or managers.

We could perfectly use the administration interface to do these
operations. It is a convenient thing to do at times (when doing
development, to quick-check things). But it is not recommended beyond
that because it is a bit complicated to do it right and it will be
only local to your instance (or, said a bit differently, such a
workflow only exists in an instance database). Furthermore, you cannot
write unit tests against deployed instances, and experience shows it
is mandatory to have tests for any mildly complicated workflow
setup.

Indeed, if you create the states and transitions through the user
interface, next time you initialize the database you will have to
re-create all the workflow entities. The user interface should only be
a reference for you to view the states and transitions, but is not the
appropriate interface to define your application workflow.